Effects of Nose Bluntness on Hypersonic Boundary-Layer Receptivity and Stability

High-speed laminar-to-turbulent transition over blunt bodies is relevant to a variety of aerodynamic applications. Experiments have observed that beyond a critical value of the nose radius the initially downstream movement of transition location is reversed. Linear stability and receptivity analyses have been unsuccessful at predicting this reversal. The current Paper uses a random forcing approach in conjunction with the Navier–Stokes equations to understand this phenomenon using blunted flat plates of different nose radii at . Specifically, steady validated base flows are perturbed to generate multiple scales associated with both the boundary layer as well as the entropy layer. The dominant frequencies and corresponding growth rates in the frequency spectrum are identified with spectral decomposition techniques. With increasing nose bluntness, a reversal in growth rate of maximum amplified frequency is observed beyond a critical value. At low bluntness, the invariance of the scaled frequency parameter indicates that the dominant instability is the Mack mode, as confirmed with through dynamic mode decomposition. For nose radii higher than the critical value, the mode associated with the peak frequency is different, with more prominent support in the entropy layer, indicating the presence of non-Mack modes.